According to the docs on file name encryption
This uses a 32 byte key (256 bits) and a 16 byte (128 bits) IV both of which are derived from the user password.
So the key material is of constant length regardless of the length of the password.
So I really wouldn't expect a longer password to make a difference to the length of the file names.
Encrypted file names lengths are this long:
((length_of_filename+1) rounded up to nearest 16 bytes) * 8 / 5 all rounded up to the nearest integer
So a 1 byte file name should be 16*8/5 = 26 characters long.
Likewise a 128 byte file name, +1 rounded up to a multiple of 16 becomes 144, 144*8/5 = 230.4 rounded up is 231 characters which is exactly what I get when I try it...
This (128 chars)
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
Becomes this (231 chars)
25sgjm2r1ajrdl3t0grbu85gaaafohakpuk3dc07nq2gil5edb822u556h0i1pl2fs901pjb6fnvke5utpne1p41j09i9q1e56h7t6tq1pqkcc9ulhbjoickvbdfkmpmq348rnf9pltcdv5apbemqgprddhve8jc33qov7opurr325k5057mk3tebtef957utpujvt4rc7jovuogobf6iucl6p47np9adp4n29g"
Note that if you have unicode characters, eg é then these take up more than one byte and will bring the total length down.