Its not going to be proportional, even if it may look like that temporarily at first. You would be wise to start reducing your mining operation if you are already large (diversify your portfolio, invest elsewhere, or go solar/wind instead of pure asic mining purchases).
If bitcoin is 8k at the time of halving, don't expect it to go 16k next day, something like 12k or less would be about right.
That is without taking into consideration even more efficient miners rising that diff up. In the aftermath price might be even go down and kick a bunch of miners out (again). It is also wise to not spend everything, keep reserves. Don't live on the margin like most miners do, if you are unable to survive without a PPS pool administering your profits, then you are in trouble.
I think you are accurate to think the most profits will be made right before the halving, then assume some slump afterwards before things become attractive again, but not as much as the previous halving.
I might have agreed with you about reducing my operation instead of maxing it out if we were maybe 3 months away. Taking into account Diff adjustments and everything else I stand to have my little farm paid for well before the halving. This way I can weather the storm and see what happens. Not to mention I run free in the Winter for anything I can get into my house ~ 60 Amps. That was the part about being able to do something forever.
I definitely don't expect anything to happen over night but I'm expecting a weird 6 weeks with a lot of unknowns at play. I con't mine PPS and don't expect that to change anytime soon unless they choose to shutdown for some reason; which is unlikely. Diversifying is always good advice, even that though carries the same risks, I have a small spread of crypto and plan on keeping it that way. Either way we'll see what happens, I'm more interested in seeing the overall event and effect than worried about future plans.