What Pot Size for my next Grow. 80x80cm Tent Size, currently using 11L fabric Pots, not happy with size of plants and fear less yield

11L is fine for a plant with limited vege time or an autoflower. You can look after a grow and assess the rootball and roots... is it wrapped around the outside of medium in a severe way? should have some limited amount of that after 3months or more, but if extreme that's a sign of the pot being too small. Fabric pots will mitigate this longer with air pruning occurring. Rootbound plants are obvious. You give them a formula that works well and they will start to struggle with leaf symptoms that you can't control with any adjustments. a soilless/hydro nutrient line would help in this regard, but only for so long. it too will run into the same problems just as fabric pots will evenetually, too. faster growth will occur with a soilless/hydro method, if not doing that now. will get more growth in same amount of time... or same growth in less time. depends on your goals. Without the need for microbes and such to make certain nutrients plant-available, you can more easily feed a plant more efficiently relative to its growth rate, so you typically gain in that regard, if done right. Going over-sized can be a problem too.. extra waste and potentially extend the time between irrigations too long if the plant can't drink fast enough relative to the size of the pot, which isn't good for the chemistry of the medium as well as a vector for disease. 1month per cubic foot pot size... or 1 gallon per foot of height are general suggestions that are repeated and seem to work okay. I've grown plenty of large plants in a 3-gal.. it's not all the pot's fault. If in soil or any other number of factors... vege time being the easiest thing to change for a photoperiod, and just one more reason never to buy autoflowers, lol.