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

t=int(input())
for _ in range(t):
    n=int(input())
    l=list(map(int,input().split()))
    m=max(l)
    s=len(set(l))
    if s==1:
        print(-1)
    else:
        i=0
        while i<n:
            if l[i]==m:
                if  i<n-1 and l[i]>l[i+1]:
                    print(i+1)
                    break
                if i>0 and l[i]>l[i-1]:
                    print(i+1)
                    break
            i+=1
        
