Shy pair of angels?

I recently received a pair of koi angelfish and put them in my 55g. The only other inhabitants are 4 lamp eye tetras and a 5" hifin pleco. The pair seem to only stay on the right side of the tank where there are larger plants and a large cave for them. If I move the plants or planted the tank thicker would they move around more? Temp is usually 76 in all of my tanks. Would removing the tetras and/or switching to corys help? Thanks!

Yeah I figured new-tank shyness...I just love to ask too many questions in addition to reading lol. Can't have too much good advice. Thanks a lot as always!