it is not what its block .. it is how bushy and low you can keep the plant and also how even you can keep the canorby ..
think about it .. if you just let it shoot up at the light it will only be the very top of the main cola that get real light .. if you make your plant a bush/bonsai with many shoots you will spread out the canaby .. that way have like me 12 shoots with bud sites close to the light ..
yea they will be smaller in size .. maybe I only get half or even 1/4 of one of them as 1 main colar .. but multiply that with 12 .. plus all the side shoots on 12 main steams insted of one .. easily double your haverst Im sure ..
and just as a advice I somehow think I need t give here ? .. dont pull any fan leaves off it to get light down .. maybe bottom 1/4 down (last few inches that dont get light) later on befoe flowering .. need good air flow down ther and need to make the plant consentrait on the buds at the tops ..
light .. nomather if it is CLF .. T5/T8 tubes .. HPS or MH loose light dramaticly at distance .. not like the sun out side .. like evry time you go a foot away you loose 4 time (or its only 1/4 as strong)
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and dont FIM/top your plants agin right after ... you can do it agin .. and maybe even a 3Th time .. if you Veg for long .. but it needs time to recover (2-3 days) and then time to shoot up agin (maybe a week or two) maybe after the new once have 3-4 new nots you could do it agin ..if you realy want it bush with small bud sites ..
I did only FIM it once and got 12 shoots in total .. 6 main and 6 more on the side .. did just LST them out to make room for more growth in the middel and to keep a even canaby ..