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

for t in range(input()):
    n=input()
    a=map(int,raw_input().split())
    maxi=max(a)
    idx=-2
    for i in range(n):
        if(a[i]==maxi):
            can=0
            if(i-1>=0 and a[i-1]<a[i]):can=1
            if(i+1<n and a[i+1]<a[i]):can=1
            if(can):idx=i    
    print idx+1            