They definitely like a jungle of plants, and things to explore! So I definitely recommend adding plenty of plants and other things they can perch on. That slate cave thing on the left side of my pygmy tank (doesn't have guppies in it now) is a favourite place for mine to sit on top of and chill as a group, and since I prop the top end up on the larger river pebbles, the tiny fry also like to hide underneath it. I imagine that as well as feeling safe and secure, it's also where mulm, and thus, micro-organisms gather.
They are a curious and playful little fish, so keep the tank interesting by adding small tettacotta pots, an interesting wood piece, some almond leaves, things like that.
Having said that, behind the sponge filter right at the back and deep into the plants back there is where mine all dive to if they're spooked, or I'm doing WCs etc. And they're easily spooked! Remember that the more there are, the more secure they feel, but also the more eyes are watching for any trouble! If one panics and dives for cover, the others will too. But mine usually calm and come out again pretty quickly, so I'd wonder too if they're nervous about the larger fish. Mine did used to swim with and follow the guppies at times, but I've never kept them with anything larger than that either. If adding more plant cover/visual tank interest doesn't work, perhaps trial the tank without the larger fish if that's possible (if you have a quarantine tank or something) and see whether that makes a difference in their behaviour?
Also, is the tank in a high traffic area perhaps? Mine is in a quiet corner, so as long as I sit a good distance away, or sneak up on them slowly so they don't spook too much, they come out and swim in the open water or feed on the beach again. Perhaps they are coming out to play when you're not seeing them, but spook and hide if you coming into the room startles them?
11 is a nice number of them to have, so that's a great start! Please do keep us updated, love these little fish so much! Hands down my favourite to watch, don't even know how many I have! Just know I started with seven, and there must be 30 or more in there now. They're constantly spawning, and I'm constantly finding new fry when I water change, or spotting a mini one joining the adults as they swim together. Gorgeous little fish!