I'm with Alpari Uk & fixed spreads. They seems to be smaller than yours (as I see in your post with calculations): EU 1.6, GU 2.5, AU UC 2.6, AU 2.8, EJ 3.2 etc.
Anyway, answering your question, I think that spread doesn't affects the overall outcome, because the answer is: my analisis of direction is wrong....
I have to thanks you forever 
, because you gave me a better knoweledge about how the market moves

I was just considering (before reading your thread) naked trading using price action (peaks & walley and so on), but there was always an obscure reason behind the up and down of the moves... whipshaws (in any timeframe.....) are always there to confuse each kind of analisys.
You gave us, instead, a clearer view of the whole movement, and a simple rule to get in & eventually out! (Incredible: just few posts ago, I did understand nothing.....

)
There will be losses, of course (expecially in hard trending days, where 20 pips bounces are just little retracements of big trends), but nobody here is looking for the Holy Grail. We just need an edge to win more than we loose, and I'm sure you've found this edge!