Hi sunny03,
IMHO, in order to let the cluster LED cover the entire tank, you have to look into a few factors such as,
1. LEDs per cluster
2. Design and position of the LEDs per cluster
3. Type and colour of the LEDs used & colour combination
4. Degree of Len used
5. Coverage area per cluster
For example, I have 1 Radion on my 3ft tank and I have the situation like you because 1 Radion can only cover 2x2ft. Currently I'm using previous DIYed LED module to cover the other part/side of the tank but problem is... difficult to blend in with Radion colour temperature even though I controlled with ProfiLux light II controller.
For 3ft tank, I need at least 54 LEDs to cover the entire tank but Radion has only 2 clusters (17LEDs/Cluster) which is shortage of 20 ++ LEDs.
Therefore, this new LED cluster is basically designed to match & compensate the loss light that Radion unable to cover and at the same time add UV/TV to create more fluorescent effect cum improve coral growth in my tank.