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

from math import *
t=int(input())
for u in range(t):
    #w,n=map(int,input().split())
    
    n=int(input())
    a=list(map(int,input().split()))
    mx=max(a)
    
    ind=a.index(mx)
    out=-2
    for i in range(ind,n):
        if i>0 and a[i]==mx and a[i-1]<mx:
            out=i
            break
        if i<n-1 and a[i]==mx and a[i+1]<mx:
            out=i
            break
    print(out+1)
    
            
    
