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 i in range(t):
    n=int(input())
    a=list(map(int,input().split()))
    a1=set(a)
    if len(a1)==1:
        print(-1)
    else:
        a2=max(a)
        if a[0]==a2 and a[1]!=a2:
            print(1)
        elif a[-1]==a2 and a[-2]!=a2:
            print(n)
        else:    
            for j in range(1,n-1):
                if a[j]==a2 and (a[j+1]!=a2 or a[j-1]!=a2):
                    print(j+1)
                    break