You need one on the back wall and one on the L and R sides. In ES mode you will designate each one by position (side or back). You do not have to have all 40s. The MP10ES and the MP40 ES are fully compatible programing wise. You can use an MP10 for the back wall, but remember the 10 only goes to 3/8" thick glass.
Apparently you cannot use an MP40W (or MP10W) in Ecosmart mode, but you can in all other modes. From the Owner's manual:
>Use of EcoSmart drivers with a Wireless Wave Driver (WWD)
Your EcoSmart driver is capable of communicating with a WWD equipped MP40w. However, the WWD equipped pump will not have the luxury of communicating with your EcoSmart driver in any of the EcoSmart modes. Therefore, your WWD equipped pump will not run in any of the EcoSmart slave modes outlined above. If you have a WWD equipped MP40w and wish to achieve the full benefit of using the EcoSmart modes, we recommend that you purchase an EcoSmart upgrade kit for your pump, available through our online store at http://www.ecotechmarine.com">www.ecotechmarine.com</a>.
However, your WWD and EcoSmart pump are capable of communicating with one another in any of the modes except for EcoSmart modes, such as Constant Speed Mode, Random Modes, Short Pulse Mode, Long Pulse Mode. Your WWD can also be told to go into Feed Mode or Night Mode by an EcoSmart driver.>