Best strategy is definitely to fill all but the last two spaces with miners and fill the last two with stabbers. Could probably go for one stabber and have an extra miner, but that's a bit riskier I would think.
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I suppose it's probably obvious, but enemy variety needs to exist to shake up my strategy. As it stands, a stabber will trade with zombies at about a 1:1 ratio.
Basically, I would want reasons to use something other than a stabber.
Also, I guess more lanes would be interesting or longer/shorter lanes.
Different things that may force you to change strats up.
I would assume Plants vs Zombies has some interesting ideas in that regard. I wouldn't know. Never played it.