I think most people are using creepers with casters (rollers) but I am not. This would also affect your leverage as well. My way of going underneath the vehicle 100% of the time is using a "magic creeper" and this allows me to not only be flat against the floor but I also don't need to jack the vehicle that high to access anything.
My Body Position (Example)
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Inner/Outer Splash Shield + Wheel Splash Shield Removed
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Tensioner: I crouched in wheel well to simply relieve its tension and replace serpentine belt.
Water pump belt: I used a creeper and kept rolling away lol. I must've used a towel to keep creeper in place. Laying on creeper gave me leverage to be able to push the belt into pulley. Did you use a tool or simply pushed it in with your hand?
Removing entire wheel well shroud sure gave extra space.