Auto only cameras are tricky. I'm not too familiar with Yashica Electro 35 GSN, but I think it has light sensor outside the filter, right?
So the light meter is seeing the visible light, and the film is seeing only IR. The amount of IR light is not proportional to that of visible light... it really depends. When the sun is up with no cloud, you can probably meter for ASA 80-125 range without filter and exposure HIE with your filter. But I recommend to bracket by +2 and -2 stops, at least, though, since this guestimate can be off by a few stops.
Incidentally, I was once thinking to modify one of the cheap Sekonic meter to see only IR light... to make my life easier

but the meter I bought for this project gets used for other purposes so I can't modify it any more

I have the photographs of the inside of the meter on my web, though.