I have a question regarding the J-20's EOTS. Why is it only forward pointing while the F-35's EOTS is 360deg?
If you see the pics, the rear half of the J-20s EOTS is obscured.
It's understood - not known! - to be an a2a-optimized far- infrared(or dual band?) long-range a2a search set. IIRC we don't know if it includes laser or other heads; if the proposed F-22 IRST is an indicator - it may not. The lack of need to rotate 360 allows for the largest possible main mirror (simple geometry).
F-35 EOTS is a multirole, but really ground attack-optimized hardware, combining med- infrared sensor with a video feed and LRF/designator. IIRC you can treat it basically as an internal variant of SNIPER ATP (ATP-SE?).
It needs to be able to look back, because this is how free-fall laser-guided bombs are used (or even propelled a2g munitions, if the aircraft turns away after drop).