1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

# -*- coding: utf-8 -*-
"""
@author: coding_don
"""
import math
import sys
if __name__=="CP":
    sys.stdin = open('ip.txt', 'r') 
    sys.stdout = open('op.txt', 'w')

try:
    
    def main():
        t=1
        t=int(sys.stdin.readline())
        while(t):
            n=int(sys.stdin.readline())
            
            a=list(map(int, sys.stdin.readline().split()))
            ans=-1
            mx=max(a)
            for i in range(n):
                if(mx!=a[i]):
                    continue
                if(i>0 and a[i-1]!=mx):
                    ans=i+1
                if(i<n-1 and a[i+1]!=mx):
                    ans=i+1

            sys.stdout.write(str(ans)+"\n")

            t-=1
        
    main()
     
except Exception as e:
    sys.stdout.write("ErrOR : "+str(e))