Yes the app name must match to a current application from seti.
 
In the boinc manager the gpu application will state what it's using. Below is typical.

As you can see I'm leaving a core open because GPURID is telling me it's using 0.986 cores of the cpu. So I'm running 3 of 4 cores on SRBase. Often it doesn't use as much as it says but playing it safe. You can tweak it even more with app_configs but that is really trial and error. bcav is the best trial and error guy here.

You can find a lot of app_config.xml Files here.
https://forums.evga.com/search?searchid=1344403&phrase=app_config.xml&high=app_config.xml
Do not Create the Folder and create the app_config.xml add the Project from BAM! or without and after the Client has been added then create the app_config.xml file.
Not everyone uses BAM! I use it myself.
Each app_config.xml is different like this is what I use for http://www.enigmaathome.net/
This Project uses 1 Full Thread or Core so <cpu_usage>1.0</cpu_usage> setting is not really needed but I set it mine
This Setting <gpu_usage>0.5</gpu_usage> will run 2 Tasks on Each GPU on the Host
 
ProgramData\BOINC\projects\www.enigmaathome.net 
<app_config>
   <app>
     <name>enigma_cuda</name>
     <gpu_versions>
         <gpu_usage>0.5</gpu_usage>
         <cpu_usage>1.0</cpu_usage>
     </gpu_versions>
   </app>
</app_config>
 
Under (Drive):\ProgramData\BOINC\
Create a file called cc_config.xml and put the below in
 
<cc_config>
 <options>
 <report_results_immediately>1</report_results_immediately>
 </options>
</cc_config>
 
The rest can be removed from this file
Other app_config.xml I use
 
 ProgramData\BOINC\projects\boinc.thesonntags.com_collatz
<app_config>
   <app>
   <name>collatz_sieve</name>
     <gpu_versions>
         <gpu_usage>0.5</gpu_usage>
         <cpu_usage>0.1</cpu_usage>
     </gpu_versions>
   </app>
</app_config>
 
This is Heavy CPU Project that uses the GPU but very little and you can run as many Threads that your CPU has.
ProgramData\BOINC\projects\sech.me_boinc_Amicable
<app_config>
   <app>
   <name>amicable_10_20</name>
     <gpu_versions>
         <gpu_usage>0.2</gpu_usage>
         <cpu_usage>1.0</cpu_usage>
     </gpu_versions>
   </app>
</app_config>
 
 ProgramData\BOINC\projects\milkyway.cs.rpi.edu_milkyway
<app_config>
   <app>
     <name>milkyway</name>
     <gpu_versions>
         <gpu_usage>0.3</gpu_usage>
         <cpu_usage>0.1</cpu_usage>
     </gpu_versions>
   </app>
</app_config>
 
ProgramData\BOINC\projects\www.gpugrid.net 
<app_config>
   <app>
     <name>acemdshort</name>
     <gpu_versions>
         <gpu_usage>1.0</gpu_usage>
         <cpu_usage>0.2</cpu_usage>
     </gpu_versions>
   </app>
   <app>
     <name>acemdlong</name>
     <gpu_versions>
         <gpu_usage>1.0</gpu_usage>
         <cpu_usage>0.2</cpu_usage>
     </gpu_versions>
   </app>
</app_config>
 
ProgramData\BOINC\projects\moowrap.net
<app_config>
   <app>
     <name>dnetc</name>
     <gpu_versions>
         <gpu_usage>1.0</gpu_usage>
         <cpu_usage>0.5</cpu_usage>
     </gpu_versions>
   </app>
</app_config>