Coir holds a lot of water, plus, if it's finely textured, it can pack pretty tightly. It doesn't appear to have any of the antomicrobial properties of peat.
Perlite isn't antiseptic, but it's theoretically sterile, and you could always sprout your seeds in pure perlite, but you'd also need to transplant them when they're a couple of inches tall.
Try a 50-50 perlite/coir mix, also try a taller container, which will keep the top layer of mix well out of the standing water table that is in every pot.
Dampen the mix, tamp it lightly to level the surface, sow the seeds 1/4-3/8" deep, then water once after sowing with a fine spray/mist nozzle. You shouldn't have to water again until they sprout, if they've been stratified adequately.
Or you could fill the bottom of the container with your 50-50 mix, and use pure perlite for the top inch. Perlite isn't that good of a growing medium on its own, (poor ion-exchange) so having some real mix below will let the roots quickly find a better growing environment. Since pure coir has no available nutrients, you'll need to feed with a complete fertilizer as well as a calcium-magnesium supplement when they're an inch tall or so.