Stunted autoflower plant

I don't see stunting but i do see the start of a nitrogen deficiency. try feeding a bit more -- mostly amping up N but the whole thing may need a slight 5-10% boost if growth has been generally slow. your watering habits look suspect too. SOP for soilless - which coco is, it's not 'unique' in any way. 1) fertigate every irrigation with well-balanced and complete diet and 10% runoff waste water - this water is fine for outdoor garden use but not for potted plants. 2) wait for acceptable dryback 3) repeat. If not doing that, it is very likely a contributing cause to slow growth. The entire volume + 10% extra... never less. Like others said you need more perlite in that coco. 33% for coco. 50% for higher water capacity substrate choices, like sphagnum peat moss. When constituted corerctly no matter what you choose to use they all will hold roughly the same water per volume and have the proper gas:water ratio in the substrate. This probably isn't a huge hinderance to growth but would impact it slightly. when properly constituted it also eliminates the potential to overwater under any common sense context of gardening.