No. Keep the suggested spacing. Too dense causes problems with airflow, light, etc. I Learned the hard way. If anything give extra space because hopefully your hydro plants will grow great!

Thinning is not something I do well. Hate it!!! So this year I decided to germinate the lettuce seeds on a damp paper towel inside a ziplock bag. Waited a day or two and gently lifted the cracked/germinated seedling into its own rock wool cube! I was then able to plop each cube into a bed of perlite, fed by a flood and drain. Results so far are great!

For production value of having a quality head of lettuce I suggest having one plant per cell and have a minimum spacing of six inches between cells or lettuce plants. Having more than one plant in the same space causes a battle among the roots for nutrients and the shoots or leaves begin to search for light and air causing strange growth patterns. Having more that one plant in a cell is possible but can look unorganized and does not provide quality plant structure and growth time length.