The 1-isomer is the generally favoured product as it is formed via a less energetic intermediate, whereas the 2-isomer is formed via a more energetic one.

The stabilization of the 1-isomer intermediate is due to the higher extent of resonance. Substitution Reactions of Polynuclear Aromatic Hydrocarbons^[1] nicely sums up the point.

Substitution usually occurs more readily at the 1 position than at the 2 position because the intermediate for 1-substitution is more stable than that for 2-substitution. The reason is that the most favorable resonance structures for either intermediate are those that have one fully aromatic ring. We can see that 1-substitution is more favorable because the positive charge can be distributed over two positions, leaving one aromatic ring unchanged. Only one resonance structure is possible for the 2-substitution intermediate that retains a benzenoid-bond arrangement for one of the rings.

1-substitution

2-substitution

But as the size of the substituent increases there is one more factor to consider. As the substituent becomes bulkier, it's steric hindrance with the hydrogens of the neighbouring carbons increases.

This is an issue for the 1-isomer as it's steric interaction with the neighbouring carbons' hydrogen is way more than it's 2-isomer counterpart. This causes the 2-isomer to be the preferred product when the substituent is bulkier.

Following is an excerpt from intermediateorgchemistry's article^[2] about naphthalene:

There is one other factor that will also effect the position of the substitution; that is the size of the group being added. In the case of large groups the ß position is favoured. This is a case of steric hindrance with the hydrogen's on neighbouring carbon atoms.

Reference:

[1]: Roberts, J. D.; Caserio, M. C. Substitution Reactions of Polynuclear Aromatic Hydrocarbons
https://chem.libretexts.org/@go/page/22330
(accessed Jun 12, 2021).

[2]: Naphthalene
http://www.intermediateorgchemistry.co.uk/aromatic1.htm
(accessed Jun 12, 2021).

The 1-isomer is the generally favoured product as it is formed via a less energetic intermediate, whereas the 2-isomer is formed via a more energetic one.

The stabilization of the 1-isomer intermediate is due to the higher extent of resonance. Substitution Reactions of Polynuclear Aromatic Hydrocarbons^[1] nicely sums up the point.

Substitution usually occurs more readily at the 1 position than at the 2 position because the intermediate for 1-substitution is more stable than that for 2-substitution. The reason is that the most favorable resonance structures for either intermediate are those that have one fully aromatic ring. We can see that 1-substitution is more favorable because the positive charge can be distributed over two positions, leaving one aromatic ring unchanged. Only one resonance structure is possible for the 2-substitution intermediate that retains a benzenoid-bond arrangement for one of the rings.

1-substitution

2-substitution

But as the size of the substituent increases there is one more factor to consider. As the substituent becomes bulkier, it's steric hindrance with the hydrogens of the neighbouring carbons increases.

This is an issue for the 1-isomer as it's steric interaction with the neighbouring carbons' hydrogen is way more than it's 2-isomer counterpart. This causes the 2-isomer to be the preferred product when the substituent is bulkier.

Following is an excerpt from intermediateorgchemistry's article^[2] about naphthalene:

There is one other factor that will also effect the position of the substitution; that is the size of the group being added. In the case of large groups the ß position is favoured. This is a case of steric hindrance with the hydrogen's on neighbouring carbon atoms.

Reference:

^{(1) Roberts, J. D.; Caserio, M. C. Substitution Reactions of Polynuclear Aromatic Hydrocarbons https://chem.libretexts.org/@go/page/22330 (accessed Jun 12, 2021).}

^{(2) naphthalene http://www.intermediateorgchemistry.co.uk/aromatic1.htm (accessed Jun 12, 2021).}