Practice mode dps never flatlines (Please read)

So I don't know if this remains true for all champions But I was doing some damage testing on aatrox specifically looking for optimal dps, and I decided the best way to go about this was to let the dps flatline and compare from there. The issue is that the DPS number on the practice dummies is not flatlining. It's been almost an hour and reliably the DPS will drop over time. At first in large numbers and quickly but the lower and longer it goes on for the slower the damage drops. But so far it has been totally reliable. A part of this may be the fact that I have guinsoo's rageblade. I would like to test other champions other than aatrox, But I am hesitant to lose the progress in my aatrox test to see if It ever does flatline.

Is this something up with the math applied to how pracice dummies take DPS? Notes: Capped attack speed, using refreshing health, refreshing cooldowns, and refreshing mana and energy, I don't know if any of these are affecting it but it shouldn't. I have aatrox W in the damage form, and the setup currently has aatrox landing the empowered strike on the dummy without jumping over it with guinsoo's passive. I encourage testing on different champions with or without the build while I continue the basic aatrox dropping DPS test. I will leave the game overnight and see if the DPS has further dropped over that time.

Noteworthy things with your tests, until i return with more information it is worth assuming if your dps is dropping at all it will continue indefinitly. Perhaps to 0? But would take many days at the decrease rate I see right now. I am not really up to the task but if anyone would like to set this up to test I would appreciate the results.