New Post: Creating Index Partitions using AutoSPInstaller

You are right. 3.87 version doesn't know how to handle more than 1 partition. I typically add them manually after the install via PowerShell. This will be about 6 lines of code.

Something close to the following should help you create Index Partition 1 on your 3rd and 4th server (WFE2 and WFE4)

Add-PSSnapin Microsoft.SharePoint.PowerShell

$WFE1="WFE2"
$WFE2="WFE4"

$ssa = Get-SPEnterpriseSearchServiceApplication #Assuming you have a single Service application
$active = Get-SPEnterpriseSearchTopology -SearchApplication $ssa -Active
$clone = New-SPEnterpriseSearchTopology -SearchApplication $ssa -Clone –SearchTopology $active

New-SPEnterpriseSearchIndexComponent -SearchTopology $clone -SearchServiceInstance $WFE1 -IndexPartition 1
New-SPEnterpriseSearchIndexComponent -SearchTopology $clone -SearchServiceInstance $WFE2 -IndexPartition 1

Set-SPEnterpriseSearchTopology -Identity $clone