It's a gamble with clams, sad to say. Injuries to the byssal organ or stress from shipping can take a while to finally take out the clam, when you finally get it. Starting with a healthy clam in the first place is half the battle, and the other half is to read the clam's behavior in the tank and help it settle in as fast as you can. If the clam kicks itself off constantly, that was already a sign that it did not like its location. As Yuki also said, if the clam is not placed in a stable spot, the closing action could also knock it off, they propel water pretty rapidly when they close.
Those blue Maximas seem to also need as much light as a Crocea would, they come from shallow regions where light is quite intense. Light starvation is also a gamble to deal with too, but I like to err on the side of giving too much light and just hit them as hard as I can with light. If it kicks itself off, I then try to place it on a frag tile on the bottom of the tank. Once it starts to lay byssal threads, I know that I've gotten the sweet spot. With too little light, you may not find out until the last few days of the clam's life, when it's too late to save it.
I've dealt with tons of clams in trying to figure them out, and of all of them, I've yet to have a Maxima that's stayed alive in my tank for longer than a month, despite getting the other species to grow like no other.
Oh, as far as flow goes, yes, you don't want to whip the mantle around, but if you don't mind re-aquascaping, just place some rocks as a guard, to create a region of gentle current for the clam to sit around in. This is what I do for the clams that sit up top, and I have two Gyres ripping hurricanes around the tank. The mantle gently waves about, but so long as it doesn't constantly push the mantle inwards into itself, you will be fine. Another technique is to place the clam so that the direction of flow pushes along the length of the clam, versus pushing against one side, this will help mitigate mantle flapping. This is what I do for the sand dwelling clams.
