Retainers and item rarity

I got both my retainers at lvl 60 a couple days ago (smn/war) with ilvls 239/243. I keep spamming quick exploration and everytime they finish i get the message "Current retainer gear should increase chances of finding rare items".

If i increase their ilvl even further will the chances increase more?

Thanks in advance,

yes i think i say power them up more :) the best bet is to google it just to be safe