TEMA RCB-4.62 sets the limits for RHO.v^2. You use the formulae in RGP-RCB-4.62 to calculate the two areas (shell and bundle) based on where you are intending to put the impingement plate, and its diameter. Use each calculated area separately and in turn to calculate v and thus RHO.v^2. If it exceeds the TEMA limit you may have a problem as it is unlikely that you will be able to adjust either of the impingement plate variables (height under nozzle and diameter) in your favour.