AOB Help

[ChocoChappie]

Hi everyone!

I hope someone here can help. I've been learning today how to use the RAOBF targetting system in SH5 WOS. I'm pretty sure I've got down the range and speed using Opical Length & Mast but can't for the life of me nail down the right AOB everytime. I have done the exact same calcs repeatedly against this ship/save and I've only hit it correctly twice out of countless attempts.

I'm measuring the mast at around 3.0 (and tried lower in the attached picture but with bad results). I've understood that if the target ship is going away from you, that you need to calculate 180-AOB. Quite often however, my calculations using the RAOBF cause my AOB to be higher than 90 degrees.

https://imgur.com/89lFBHd

The Green Arrow is the direction of the target. Yellow arrow is with the mast height & range calcs at 3.0 and 3400m respectively. The Orange and green dots are where my AOB has been before.

My question is: What do I do when the AOB is past 90degrees (like the arrow and coloured dots) and thus blank? My optical length measurement was 14 on this run.