Prop shop comp question

So i was planning on applying to several prop shops in NYC (i understand Chicago is where its at for this scene but unfortunatly my reluctance to move away from the NYC/tri-state area will make this much harder) and have a couple questions regarding comp.
Through my research i have realized that comp is much more performance based than base-pay based (a lot of places only having performance pay). I have two questions:
1.) I realize that the performance based pay is based off of ur P&L, but heres what I dont get. How often is that calculated? Since its essentially ur salary, i'd imagine its pretty often, like every week maybe? Im just a little confused because lets say its calculated every friday, wouldnt that just mean you trade very aggresively at the beginning of the week, and if you do well essentially just sit on your hands so you dont risk wiping out your gains until P&L is calculated, and then repeat?
2.) Obviously if you're losing money you wont be getting paid and will eventually be let go, but my question is could you ever be held personally liable for losses you've generated, or does the buck stop at you not getting paid/ fired? Im down with no base pay, etc. but i dont think im interested if I could be held liable for losses. Hell, then id trade my own money and take 100% of the profits as opposed to 40%ish or whatever it is, lol.

Sorry if these are dumb questions and/or already answered else where. Thanks in advance for any thoughtful responses.