I don't know the title is correct for my desire question or not tho I will try to explain as much best to make my question understandable. As we all know there are so many rhythmic note which work with time as a beat. We all are familiar with a word that is "Every first note of a beat is accented a 'downstroke'". As some few example some notes like two eight note has "1 +' as a count where (1 - downstroke / + - upstroke ) and on triplet of eight note has "1 + a" or "1 trip let" where ( 1 - downstroke / + - upstroke / a - downstroke). We can see every first note are treated with downstrokes first and the up and the down and so on. If one has appear first then automatically the other take second place and not the same stroke take place twice in a row. Is this all upstroke and downstroke are fix for a certain note or we can manipulate those strock as we wish depending on what accent we want? As we know a eight triplet has '1 trip let' where 'down-up-down' but at sextuplet which is also a triplet of two sixteenth note count being '1 trip let and trip let' has 'down-up-up-down-up-up' where one triplet is treated as 'down-up-up' which is different than same eight note triplet which has 'down-up-down'. So, what is reason behind this all downstroke and upstroke of any note? How can one manage to keep exact upstroke and downstroke which are as if meant to be for only that certain note? I hope you all understand now what I really mean to know about.
Downstrums are different from upstrums, in that the former usually have more 'body', due to them starting with hitting the lower strings first. Upstrums are more often lighter, starting with the thinner strings, and not even playing all six on the way up.
Obviously, after each down, there has to be an up. Whether this is a strummed up or a ghost up will depend on the rhythm and the player. It could even be a muted upstrum.
The point you make about a sextuplet isn't a practical one. It makes more sense to keep the down/up/down/up pattern for the strumming hand/arm going. This means that the second three of the sextuplet is an upstrum. To emphasise it is important, so it needs to be more of a full strum.
Basically, a good rhythm guitarist will keep the hand/arm in a steady down-up pattern, and hit (or miss) the strings accordingly. Patterns that use what you suggest in the sextuplet strum don't work particularly well.