asp.net web api: IIS8 - (413) Request Entity Too Large

Question

I have asp.net web api application hosted in IIS. This app has 100mb in <httpRuntime maxRequestLength=... and in <requestLimits maxAllowedContentLength=.... But sometimes client gets 413 Request entity too large in resoponse for quite small requests. I saw some fixes like "just change uploadreadaheadsize". But actually for me this solution is not clear. Why do I face this error when request limits are configured properly?
Update1: one more detail - this app uses client certificates authentication.
Update2: I found this https://technet.microsoft.com/en-us/library/cc737382(v=ws.10).aspx

Answer 1

Here you can find a description of reason for this problem. I set uploadreadaheadsize to 1 mb instead of default 49152 b. I used this powershell script:

Set-WebConfigurationProperty -pspath 'MACHINE/WEBROOT/APPHOST'  -filter "system.webserver/serverruntime" -name "uploadreadaheadsize" -value 1048576

Actually I think this script should work too (it's not so global):

Set-WebConfigurationProperty -PSPath "iis:\Sites" -location "sitename here" -filter "system.webserver/serverruntime" -name "uploadreadaheadsize" -value 1048576