Strange behaviour phrase suggester

Hi all I'm using phrase suggester to obtain spell check corrections over
user query. I have on my corpus the next words

spider, spyder, spade, spde

I want to get suggestions for spider and I'm entering next query,

"suggest" : {
"spell_ngram" : {
"text" : "spider",
"phrase" : {
"field" : "spell_ngram",
"size" : 5,
"confidence" : 0.7,
"max_errors" : 0.9,
"gram_size" : 5

  }
}

}

The output is
spell_ngram:
[
1]
0:
{
text: "spider"
offset: 0
length: 6
options:
[
3]
0:
{
text: "spade"
score: 0.15242973
}

1:
{
text: "spde"
score: 0.077127695
}

2:
{
text: "spider"
score: 0.07542856
}

}

}

I think that spyder should be the best one because the edit distance is 1,
is there any thing that I'm doing wrong.

Best

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