Diagnosis
This is the main challenge with any projector: fighting ambient light. The PL1 is bright, but no projector can create black out of grey wall paint in a lit room.
How to Fix It
Before buying anything, optimize your environment. 1) Make sure the picture mode isn't set to 'Eco'—use 'Standard' or 'Bright'. 2) Go into Picture settings and lower the 'Brightness' control (which is actually black level) and raise the 'Contrast'. This can help pop the image. 3) Eliminate any direct light hitting the screen/wall. Even a lamp across the room reflecting off a white wall will wash out the picture.
If That Didn't Work
Yes, a proper Ambient Light Rejecting (ALR) screen made specifically for ultra short throw projectors is the game-changer. It's designed to reflect light coming from the low angle of the PL1 back to you, while rejecting light from other angles (like ceiling lights or windows). It's a significant investment but the single biggest improvement for daytime viewing.
Heads Up
Not all ALR screens work well with UST projectors. You need a UST-specific ALR screen. A regular projection screen or the wrong type of ALR screen can cause a horrible rainbow-like color shift or hotspotting with the PL1. Do your research before buying.