Greetings from Norway, I'm a new user on this great forum!

I have done lots of reading on this forum for the past 15 years, finally it's time for me to make a post
I know there are lots of knowledgeable people here, so I hope someone can help me out.

So I want to make throat adapters to fit my 2" exit TAD 4001 to Altec 1505B horns. Question is, how long should this adapter be?
I have a pair of original Altec 30166 adapters to use with my 1.4" exit Altec 288-16G drivers. These are 190mm length.

The TAD 4001 have a 10 degree exit angle, according to my calculations the adpater would have to be approximately 130mm length to keep the same flare angle as the original.
However since the 4001 has a wider exit angle than Altec 288, maybe the throat adapter should also have a wider angle than the original adapter for a smoother transition to the horn?
In that case it would have to be even shorter than 130mm..

I'm a bit confused about this, so hopefully someone with a better understanding than me will chime in.

Regards,
Rune